The present invention relates to xe2x80x9cactive medical devicesxe2x80x9d as such devices are defined by the Jul. 12, 1993 directive 93/42/CEE of the Council of the European Communities, and more particularly to the diagnosis of respiratory frequency and amplitude disorders by such devices.
The present invention will be more particularly described in the case of active implantable medical devices such as pacemaker, defibrillator and/or cardiovertor devices that are also able to deliver to the heart pulses of low energy for the treatment of heartbeat rate disorders. It should be understood, however, that the device being implanted is not in any way restrictive of the invention, and that the teaching of the invention is directly applicable to many diagnostic and/or therapeutic types of active medical devices.
Patients suffering from cardiac insufficiency also frequently present a disturbed or abnormal ventilation (respiration) pattern. The incidence of sleep apnea is abnormally increased, and the respiratory profile is also often modified.
Among other things, these patients can present periodic ventiliation profiles with phases of hyperventilation alternating with either phases of normal breathing or hypoventilation, a disorder that is known by the name of xe2x80x9cperiodic breathingxe2x80x9d (or Periodic Breathing (xe2x80x9cPBxe2x80x9d), or of respiratory pauses, a disorder that is known by the name of xe2x80x9cdyspnea of Cheyne-Stokesxe2x80x9d or xe2x80x9cCheyne-Stokes breathingxe2x80x9d (or, Cheyne-Stokes Respiration (xe2x80x9cCSRxe2x80x9d)). The various alternate phases each have a duration in a range of a few respiratory cycles to a few tens of respiratory cycles, i.e., of a few seconds or tens of seconds (even to a duration exceeding a minute).
The diagnosis of this type of breathing is a useful action that can make it possible to follow better the patients and to adapt their treatment as appropriate. In this regard, clinical study has indeed shown that an improvement of the cardiac function can make a CSR disappear. More precisely, it has been shown that CSR disappears gradually with an improvement of the left ventricular function. The CSR can, in this regard, be considered as a symptom indicating the effectiveness of the cardiac therapy applied.
Conversely, because CSR itself causes symptoms and thus can worsen the performance of an insufficient heart, it is important to be able to detect the presence of CSR and to evaluate its significance. The reduction of CSR (either by an improvement of the cardiac function, or by another type of treatment, for example, medication) can prevent the development of night cardiovascular dysfunction, reduce insomnia and the number of night wakeups. This action can improve the diurnal function and quality of life of the patient.
One of the goals of the present invention is to propose an active medical device that is able to detect the presence of a respiratory disorder, in particular of the CSR type, and to operate a discrimination between the various types of profiles (e.g., PB or CSR), in an automatic and reliable way.
The traditional diagnostic means is by use of polysomnography, an exhaustive examination that typically requires an over-night hospitalization. Considering its cost, this examination is seldom proposed, especially in the beginning phase of the disease. Furthermore, difficulties in using polysomnography do not allow a regular follow-up that is needed to evaluate the evolution of the symptoms over time.
It is known from International Patent Publication WO-A-98/33554 to have an active implantable device medical that is able to follow the respiratory frequency by an analysis of the intracorporal impedance. However, the aim set by this device is to provide an indicator of the occurrence of a pulmonary edema, with the acceleration of the respiration rate being a traditional symptom of this pathology. This device analyzes only the respiration rate (frequency) and, lacking a fine analysis of ventilation, is not able to distinguish types of ventilation profiles, such as the PB or CSR type disorders.
It also is known from EP-A-0 493 222 and its corresponding U.S. Pat. No. 5,303,702, commonly assigned herewith to Ela Medical to have a pacemaker including means for measuring the respiratory activity of the patient, more specifically the minute ventilation, which parameter is used to control the stimulation pulse frequency.
A device in accordance with the present invention is of the type known according to the EP-A-0 493 222 and U.S. Pat. No. 5,303,702 mentioned above, i.e., an active medical device including means for measuring patient respiratory activity and able to deliver a signal representative of the periodicity and amplitude of the successive respiratory cycles of the patient.
According to the invention, the device also includes discriminating means, able to analyze the aforementioned respiratory signal and to operate a discrimination between various types of respiratory profiles.
In a preferred embodiment, the discriminating means include means for detecting an alternation of hyperventilation respiratory cycles separated by respiratory pause periods or hypoventilation periods, and to discriminate between periods of respiratory pause, hypoventilation or normal ventilation. Preferably, the means for discriminating includes means for analyzing the variations to the second order of the aforesaid signal. In particular, the discriminating means is able to diagnose a respiratory profile of Cheyne-Stokes type.
Preferably also the aforementioned respiratory signal is a minute ventilation signal, and, more preferably, can be the same minute ventilation signal that is known to be used to control the stimulation pulse frequency in rate responsive cardiac pacemakers.
The analyzing means can in particular include means able to detect peaks of the aforesaid respiratory signal and to evaluate the interval between successive peaks, and in particular evaluate the interval relative to a threshold value, to compare the interval(s) between successive peaks and to diagnose a respiratory profile of the Cheyne-Stokes type only for these intervals having a duration higher than the threshold value.
In a preferred embodiment, the comparison is operated only if the signal amplitude value is higher than a given minimal value, and/or the comparison is made only for values of intervals ranging between a minimal value and a maximum value data.
In one embodiment, the invention is directed to an active medical device of the pacemaker, defibrillator, cardiovertor and/or multisite device type, comprising:
means for measuring respiratory activity and providing a signal representative of the periodicity and amplitude of a plurality of successive respiratory cycles of a patient, discriminating means for analyzing the signal, discriminating between various types of respiratory profiles, and diagnosing a Cheyne-Stokes type respiratory profile,
said discriminating means comprising:
means for detecting in said signal an alternation of a hyperventilation respiratory cycle separated by one of a respiratory pause period, a hypoventilation period, and a normal ventilation period, and
second discriminating means, responsive to a detected alternation of a hyperventilation and a normal ventilation, for discriminating between a respiratory pause period and a hypoventilation period or a normal ventilation period by analysis of variation of a second order of said signal, said second discriminating means further comprising means for analyzing the variation of the second order of the signal by identifying a peak value of said signal and an interval between successive peak values.
Preferably, the discriminating means further comprises one or more of (1) means for comparing the interval between successive peaks to a threshold value, and diagnosing a Cheyne-Stokes type respiratory profile only for said interval having a duration greater than said threshold value, and (2) means for comparing the peak amplitude with a given minimal value and wherein the means for seeking peak values is responsive to seek a peak value in response to the amplitude value of the signal being greater than the given minimal value.
Also included may be a means for determining whether the interval value is between a minimal value and a maximum value, wherein the discriminating means comparison is operated only for values of intervals ranging between said minimal and maximum values. Further, the provided signal is preferably representative of the patient""s minute ventilation.